Fuel tanks for motorized vehicles have been used for many years. Typical fuel tanks are box-like, rectangular or cylindrical in shape and can contain from 10 to 30 gallons or more of a liquid fuel. Most of the current fuel tanks installed in motorized vehicles today are typically plastic or metallic in nature. However, fuel may be lost through joints between metal sections, from an instrument sensor port, from the fuel line leading to and from the engine, or from the fuel neck during refueling procedures. Further, in the case of plastic tanks, fuel may be lost through the plastic itself.
Recently, improvements to fuel tank technology have been directed to the manufacture of fuel tanks from thermoplastic, composite, or thermosetting materials using a variety of laminate or composite structures. One problem arising from the use of such materials in a fuel tank relates to increased permeability of fuel when compared to metal tanks.
To decrease the emission of fuel from these plastic tanks, improvements have focused on adding barrier layers resulting in tanks having multilayer walls. For example, U.S. Pat. No. 3,616,189 to Harr teaches an improved container having multiple layers including a nylon barrier film. However, the manufacture of multilayered or laminate materials often involves complex, expensive processing steps and expensive materials.
Another way to improve barrier properties of multi-layer structures involve adding specific chemical barrier materials to the surface of tanks or to the thermoplastic compositions used to make the tanks. For example, Walles, U.S. Pat. No. 3,740,258 and Shefford, U.S. Pat. No. 4,371,574 teaches that the addition of sulphonic acid or sulphonate groups on the surface of tank materials can improve barrier properties. Further, Wood, U.S. Pat. No. 5,928,745 adds a cyclodextrin barrier additive to a thermoplastic material used in at least one layer of a multi-layer thermoplastic fuel tank. While many of these systems improve barrier properties, significant improvements may still be achieved.
While the above solutions have improved the barrier properties of multi-layer fuel tank systems, these systems do not address the residual permeation problems occurring at attachment regions on the tank. Fuel or fuel vapor may escape through leak paths between layers of the plastic fuel tank or along exposed surfaces between the attachments and the overmolding.